It is well known that an increasingly important consideration in the production and use of integrated circuits (ICs or IC devices) is the package in which the IC resides. The module or casing in which the IC is packaged is an important factor in the ultimate cost, performance and lifetime of the IC. For example, as ICs become more dense, the efficient dissipation of the thermal energy generated by them becomes increasingly important in permitting their useful life to be as long as possible. Another consideration as the circuits become more dense is that the number of leads to the device and connections from the leads to the integrated circuit pads increases. This increases the complexity of construction and adds to the cost of the end product, not just in terms of increased and more expensive materials, but also increased production costs. A package which has satisfactorily addressed the need of a large number of interconnections is the pin grid array (PGA) where a plurality of pins oriented normal to a relatively flat package body gives a "bed of nails" appearance. IC devices in PGA packages have proven popular when hundreds of connections must be made.
Another factor affecting the design of IC devices is the advent of surface mount technology, whereby space is conserved on the printed circuit boards (PCBs) by mounting the devices directly on the conductive patterns of the circuit board, rather than by extending the leads through holes in the board. This technology is an additional influence in making the device and its package smaller, and making it more difficult to design a small device and package that will dissipate thermal energy readily.
Thus, a continuing goal in the art of providing electronic components such as integrated circuits is a device design that will address these multiple goals satisfactorily in an arrangement that can be reliably manufactured at the lowest cost. The lowest cost devices are those which have plastic bodies which can be molded from thermoplastic and thermoset materials.
Addressing all of these goals has proven difficult. It has been hard to surface mount a device containing large numbers of leads; devices in PGAs traditionally must either be mounted through holes in the PCB or in a carrier that is in turn surface mounted. Additionally, PGAs are generally made of expensive ceramic materials, rather than the less expensive plastic compounds. Proposed methods of surface mounting devices having a large number of connections (that is, a "low cost" PGA), often require special treatment to the outer leads, such as providing bumps of solder or gold that prove difficult to fabricate and increase the cost of what is intended to be a relatively inexpensive device. Thus, the issues of very large pin counts, thermal dissipation, surface mounting and low cost are intertwined.